1. Field of the Invention
The present invention relates to a ceramic capacitor.
2. Description of the Related Art
Hitherto, a ceramic capacitor has been used in electronic apparatuses. In general, the ceramic capacitor is mounted on a substrate using solder or the like.
In recent years, the use of a solder that does not contain lead (hereinafter referred to as “Pb-free solder”) having a high environmental load has started. However, since the melting point of the Pb-free solder is low, when a ceramic capacitor is mounted in vehicles, it has been difficult to use the Pb-free solder.
Hence, it has been considered to use an electrical conductive adhesive instead of using the Pb-free solder. As the electrical conductive adhesive used for ceramic capacitor mounting, in general, a thermosetting resin, such as an epoxy resin, containing a metal filler of Ag or the like has been used (for example, see International Publication No. WO 2009/001842).
When a ceramic capacitor is mounted on a substrate, an electrical adhesive may adhere to a surface of a ceramic base of the ceramic capacitor in some cases. In such a case, because of an electric field generated between an internal electrode located closest to the substrate when the ceramic capacitor is mounted thereon and the electrical conductive adhesive adhering to the ceramic base, Ag contained in the electrical adhesive moves into the ceramic base to cause Ag migration that reaches the end of the internal electrode, and as a result, the insulating resistance may be degraded in some cases.
In addition, when the electrical conductive adhesive is used, the outermost layer of an external electrode of the ceramic capacitor preferably contains Ag. When a high voltage is applied to the ceramic capacitor, Ag contained in the external electrode may move therefrom to the other external electrode through the surface of the ceramic capacitor, so that migration may occur in some cases.
In order to suppress the Ag migration described above, for example, reduction in the electric field to be applied to the end of the external electrode has been considered by providing a dummy electrode outside an internal electrode that is located at an outermost position in the ceramic base and by arranging a primary surface of the ceramic capacitor to face a mounting substrate. However, for example, in the case in which the ceramic capacitor has a substantially prismatic shape or the like, a ceramic capacitor mounted so that a primary surface thereof faces the mounting substrate and a ceramic capacitor mounted so that a side surface thereof faces the mounting substrate may be randomly mixed together in some cases. In the ceramic capacitor mounted so that the primary surface thereof faces the mounting substrate, although the electric field intensity applied to the end of the external electrode can be reduced by the dummy electrode, in the ceramic capacitor mounted so that the side surface thereof faces the mounting substrate, even if the dummy electrode is provided, the electric field intensity applied to the end of the external electrode is not likely to be reduced.
In consideration of the problem described above, according to International Publication No. WO 2009/001842, it has been proposed to reduce the electric field generated between the internal electrode and the electrical conductive adhesive by decreasing the size of a front end portion of the internal electrode.
However, if it is attempted to decrease the size of the front end portion of the internal electrode, when a conductive paste layer is printed to form the internal electrode, for example, oozing and/or blurring may occur, and as a result, the shape of the internal electrode is liable to vary. Hence, the ceramic capacitor thus formed disadvantageously has a considerable variation in capacity.